The incorporation of electronic devices with pneumatic tire structures yields many practical advantages. Tire electronics may include sensors and other components for obtaining information regarding various physical parameters of a tire, such as temperature, pressure, number of tire revolutions, vehicle speed, etc. Such performance information may become useful in tire monitoring and warning systems, and may even potentially be employed with feedback systems to regulate proper tire pressure levels.
U.S. Pat. No. 5,749,984 (Frey et al.) discloses a tire monitoring system and method that is capable of determining such information as tire deflection, tire speed, and number of tire revolutions. Another example of a tire electronics system can be found in U.S. Pat. No. 4,510,484 (Snyder), which concerns an abnormal tire condition warning system.
U.S. Pat. No. 4,862,486 (Wing et al.) also relates to tire electronics, and more particularly discloses an exemplary revolution counter for use in conjunction with automotive and truck tires.
Yet another potential capability offered by electronics systems integrated with tire structures corresponds to asset tracking and performance characterization for commercial vehicular applications. Commercial truck fleets, aviation crafts and earthmover/mining vehicles are all viable industries that could utilize the benefits of tire electronic systems and related information transmission. Tire sensors can determine the distance each tire in a vehicle has traveled and thus aid in maintenance planning for such commercial systems. Vehicle location and performance can be optimized for more expensive applications such as those concerning earth-mining equipment. Entire fleets of vehicles could be tracked using RF tag transmission, exemplary aspects of which are disclosed in U.S. Pat. No. 5,457,447 (Ghaem et al.).
Such integrated tire electronics systems have conventionally been powered by a variety of techniques and different power generation systems. Examples of mechanical features for generating energy from tire movement are disclosed in U.S. Pat. Nos. 4,061,200 (Thompson) and 3,760,351 (Thomas). Such examples provide bulky complex systems that are generally not preferred for incorporation with modern tire applications. Yet another option for powering tire electronics systems is disclosed in U.S. Pat. No. 4,510,484 (Snyder), which concerns a piezoelectric reed power supply symmetrically configured about a radiating centerline of a tire.
Another typical solution for powering tire electronics systems corresponds to the use of a non-rechargeable battery, which inherently provides an inconvenience to the tire user since proper electronics system operation is dependent on periodic battery replacement. Conventional batteries also often contain heavy metals that are not environmentally friendly and which present disposal concerns, especially when employed in large quantities. Still further, batteries tend to deplete their energy storage quite rapidly when powering electronic applications characterized by complex levels of functionality. Battery storage depletion is especially prevalent in electronic systems that transmit information over a relatively far distance such as from truck wheel locations to a receiver in the truck cabin. Even when batteries are used in electronics systems that transmit from wheel locations to a closer receiver location, information is then typically relayed via hard-wire transmission medium from the RF receiver location to the vehicle cab thus requiring the installation of additional and often-expensive communications hardware in a vehicle.
Yet another known method for deriving power for tire monitoring systems relates to scavenging RF beam power with an interrogation antenna in close proximity to a tire and integrated electronic features. Energy that is radiated from the antenna is scavenged to power the electronics, which must often be very specialized ultra-low-power electronics limited to within a few microwatts. Interrogation antennas employed in conjunction with beam-powered electronics must typically be placed in relatively close proximity (within about two feet) to each wheel well due to limited transmission ranges. This typically requires multiple interrogation antennas per vehicle, thus adding to potential equipment costs. Each antenna is also quite susceptible to damage from road hazards, and thus for many reasons may not be the most desirable solution for powering certain tire electronic applications.
In accordance with the present subject matter, it is appreciated that certain advantages of piezoelectric materials have long been recognized. However, such technology is constantly improving, thus potentially affording applications that utilize piezoelectric materials with improved operating capabilities. Examples of relatively new advances in piezoelectric technology are provided in U.S. Pat. Nos. 5,869,189 (Hagood, I V et al.) and 6,048,622 (Hagood, I V et al.), directed to composites for structural control. The presently disclosed technology concerns further advances in piezoelectric technology such that a piezoelectric power generating device can be integrated with a tire or wheel assembly for purposes of energy harvesting as well as tire rotation signal generation.
Currently pending and co-owned U.S. patent application Ser. Nos. 10/143,535 and 10/345,040 disclose aspects of generating and harvesting electric power from a rotating tire's mechanical energy using piezoelectric materials. The present invention concerns further applications offered by the integration of such piezoelectric structures in a tire or wheel assembly. More particularly, such piezoelectric structures can be combined with additional features to provide a self-powered tire revolution counter in accordance with aspects of the present invention.
Known existing means for counting tire revolutions involve attaching a mechanical counter to a wheel hub. Since a mechanical counter is not integral to the tire, maintaining an accurate lifetime revolution count requires accurate record keeping. Considering that some tires are often moved to different wheel positions or even different vehicles, and/or can be recapped several times, record keeping is an inconvenient, error-prone, and unreliable process.
The disclosures of all of the foregoing United States patents and patent applications are hereby fully incorporated into this application for all purposes by reference thereto. While various tire electronics systems and power generation systems therefor have been developed, no design has emerged that generally encompasses all of the desired characteristics as hereafter presented in accordance with the subject technology.